/* 返回页面顶部 */
.back-to-top {
    position: fixed;
    bottom: 60px;
    right: 50px;
    z-index: $z-index + 10;
    width: 25px;
    height: 25px;
    line-height: 1.9;
    text-align: center;
    opacity: 0;
    background: $back-to-top-bgcolor;
    color: white;

    /* 使btn出现,并可点击 */
    &.back-to-top-on {
        opacity: 0.8;
        cursor: pointer;
    }
}